FIELD OF THE INVENTION
The invention relates to a circuit configuration for the generation of a line terminating impedance.
In telecommunications, terminals are typically connected to special interface circuits through analog subscriber lines. Among other things, such an interface circuit, which is also known as a Subscriber Line Interface Circuit (SLIC), provides the subscriber line with a line voltage and a line current at a certain specified line terminating impedance. This line terminating impedance varies from country to country and thus should be adjustable, preferably in a simple manner.
If the line terminating impedance is realized using analog circuit technology, there are practically no stability problems, but changing the impedance is difficult or only possible with very complex circuitry. On the other hand, a purely digital solution would be the most favorable in terms of easy modification of the impedance because of its programmability, but a purely digital solution is not possible for reasons of stability. A final option is a partly analog, partly digital realization of line terminating impedance. Due to the complexity of the transfer function of such a system, in particular at a higher order, stabilization is very difficult.